Embodiments of the present invention relate to the generation or inspection of an electron beam pattern on a substrate.
An electron beam apparatus is capable of scanning one or more electron beams onto a substrate to generate or inspect an electron beam pattern on the substrate. A typical electron beam apparatus comprises a vacuum chamber enclosing electron beam source, focuser, and detector components. The electron beam source components generate electron beams that are modulated and scanned across the substrate to generate or inspect the electron beam pattern on the substrate.
One commonly used electron beam source of the electron beam apparatus comprises a photocathode. The photocathode has a photoemissive layer that is typically fabricated on a transparent layer. A light beam is directed onto the photoemissive layer of the photocathode to cause the photocathode to emit an electron beam, and the light beam is turned on and off to blank the electron beam on and off.
However, conventional photocathode electron beam sources often have electron current levels that undesirably fluctuate during operation of the photocathode. These electron beam current fluctuations adversely affect the operation of the electron beam apparatus. For example, poor electron beam stability can result in variable exposure levels across the substrate in pattern generation, thereby limiting the quality and resolution of the pattern being generated on the substrate. Fluctuating electron beam current levels also affect the level of precision at which a substrate can be inspected.
Thus, it is desirable to have an electron beam source and electron beam apparatus capable of generating a stable electron beam during operation. It is further desirable for the electron beam source to provide a reliable and consistent electron beam current.